Protection of underwater equipment by immersion

ABSTRACT

An improvement is disclosed in apparatus of the type including a base anchored to a submerged bottom, an elongated tower provided with a buoyancy chamber near its upper end, and a pivot assembly that connects the tower to the base and permits the tower to sway in response to environmental forces. The improvement resides in a fluid tight, open bottom housing connected to said tower and adapted to enclose the pivot assembly in a bath of a lubricant, regardless of the angle of tower sway.

United States Patent [151 3,693,362

Leonard et al. [451 Sept. 26, 1972 I PROTECTION OF UNDERWATER 3,524,323 8/1970 Miller ..6l/46.5 EQUIPMENT BY IMMERSION 3,455,270 7/l969 Mascenik et al. ..9/8 P [72} Inventors: Theodore E. Leonard, Houston,

Tex 77024; James R. uoyd Primary Exammer-Jacob Shapiro HoustonTeK 770 5 Att0rneyJames A. Reilly, John B. Davidson, Lewis H. Eatherton, James E. Gilchrist, Robert L. Graham [73] Assignee: Esso Production Research Comand James Reed [57] ABSTRACT [22] Filed: May 12, 1970 An improvement is disclosed in apparatus of the type [2] 1 App]. NO: 3652] including a base anchored to a submerged bottom, an

elongated tower provided with a buoyancy chamber near its upper end, and a pivot assembly that connects US. Cl. 1 th tower to the ba e and ermits the tower [Q sway in [5 1] Int. Cl ..E02b 17/02, 1363b 21/38 response to environmental forces. The improvement [58] new of Search 5 resides in a fluid tight, open bottom housing connected to said tower and adapted to enclose the pivot assembly in a bath of a lubricant, regardless of the [56] References cued angle of tower sway.

UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 3,5l7,5l7 6/1970 Blenkarn .6l/46.5 3,454,083 7/1969 Brooks ..l66/.5 3,500,841 3/1970 Logan ..6l/72.3 X

PATENTEHSMB m2 3.593; 362

INVENiURS Theodore E. Leonard James R Lloyd BY g A AT TORNE Y PROTECTION OF UNDERWATER EQUIPMENT BY IMMERSION BACKGROUND OF THE INVENTION protecting a pivot assembly employed to connect a lo buoyantly supported tower to its base by enclosing the pivot assembly in a fluid bath.

2. Description of the Prior Art As efforts directed toward drilling for and production of crude oil and natural gas are extended into deeper waters, depths will ultimately be reached which will make it impractical to use the rigid, bottom founded platforms presently employed to support such operations. One alternative to these rigid platforms for deep water locations is a buoyantly supported tower. Such structures generally include a base fixed to the submerged bottom. an elongated tower provided with one or more buoyancy chambers near its upper end, and a pivot assembly that connects the tower to the base and permits the tower to sway in response to wind, waves and ocean currents.

A serious problem involved in insuring an extended operational life for a buoyantly supported tower is protecting the pivot assembly from mechanical wear and adverse effects of the sea water environment. These pivot assemblies must necessarily be massive structures and normally include a universal joint or ball joint. The pivot must be capable of undergoing frequent deflections of several degrees from vertical in any direction caused by waves acting on the upper part of the tower. During storms the tower may occasionally sway to an angle of five to ten degrees. Maintenance of a lubricant between and around the sliding surfaces of the pivot during its extended operational life is necessary to minimize wear and avoid marine fouling, either of which could lead to freezing of the joint.

Pressurized lubrication of the pivot assembly has been tried in the past. High pressure systems, however, are not suitable for continuous and unattended underwater service over extended periods of time. They are subject to periodic line failures caused by rupture or plugging and to seal failures resulting from rupture or salt water seepage. Moreover, such systems do not protect the pivot assembly from the corrosive environment in which it is immersed. It will therefore be apparent that a need exists for a more reliable system for lubricating the pivot assembly and protecting it from the hostile underwater environment.

SUMMARY OF THE INVENTION The apparatus of the invention is useful in controlling the operating environment of an underwater device and will generally alleviate the problems outlined above. The apparatus of the invention is particularly useful in conjunction with structures of the type including a base anchored to a submerged bottom, an elongated tower provided with a buoyancy chamber near its upper end, and a pivot assembly that connects the tower to the base and permits the tower to sway in response to environmental forces. The present apparatus includes a fluid tight, open bottom housing adapted to enclose the pivot assembly within a bath of fluid that is lighter than water. A collector assembly is normally positioned above the bottom of the housing to collect any fluid that escapes. The apparatus may also include a means for transferring fluid from the collector assembly back to the housing.

When the apparatus of the invention is used to protect the pivot assembly of a buoyantly supported tower, a lubricant is normally introduced into the housing which surrounds the pivot assembly. The housing is preferably attached to the tower structure above the pivot and configured to permit the pivot assembly to remain immersed in the protective fluid regardless of the angle of tower sway. The collector assembly should be positioned above the open bottom of the housing so that it will trap any fluid which escapes the housing as a result of tower sway or overfilling and thereby prevent pollution of the seaway. The means for transferring fluid from the collector assembly back to the housing serves to replenish the fluid in the housing and to insure that the housing always contains sufficient fluid to cover the pivot assembly. Thus, the apparatus of the invention offers significant advantages over systems suggested heretofore by insuring lubrication of the pivot assembly while protecting it from the corrosive seawater environment.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic elevation of a buoyantly supported tower with its pivot assembly enclosed within a housing constructed in accordance with the invention to serve as a fluid bath. A collector assembly is positioned above the housing.

FIG. 2 depicts an alternative form of collector assembly for trapping fluid that escapes the housing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 depicts a buoyantly supported tower 13 installed in a body of water 11. The tower base 15 is shown anchored to the submerged bottom 17 by pilings 19. A pivot assembly such as universal joint 21 connects the tower to the base, permitting the tower to sway in response to environmental forces. Buoyancy is provided by chamber 23 positioned near the upper end of the tower. A platform 25 situated atop the tower supports surface equipment used for drilling, production and associated operations.

A fluid tight, open bottom housing 27 is shown connected to the structure in close proximity to the pivot. The housing should be constructed of an impermeable material that is insoluble in water and that is capable of retaining a fluid lighter than water, i.e., a fluid having a specific gravity lower than that of water. Preferably, the fluid will be a lubricant; however, other fluids which both protect the pivot assembly and are lighter than water can also be employed. For instance, it is contemplated that an inert gaseous environment might be an optimum medium for some pivot assemblies. While the housing shown enclosing the pivot assembly is a hemispherical shell, other configurations, e.g., cylindrical, are also contemplated to be useful. It should be noted that the housing extends downwardly to a level somewhat below that of the pivot assembly when the tower is vertical. It should also be noted that for any particular housing diameter there exists an amount of wall overhang that will insure that the pivot assembly remains in the fluid bath even when the tower sways 5 to in FIG. 1 a collector assembly 29 is shown connected to the tower at a point above the open bottom of the housing. This fluid tight assembly is constructed of an impermeable material and will collect any fluid that escapes from the housing. Thus if a fluid lighter than water, e.g., oil, escapes from the housing as a result of tower sway or overfilling, it will be trapped in the collector assembly and may subsequently be withdrawn from the upper part of the assembly and returned to the housing. The collector assembly shown is a conical shell attached to the lower part of the tower. It will be apparent that other configurations would also be suitable, provided they have a diameter sufficiently greater than that of the housing. Such assemblies should also preferably permit fluid to migrate upwardly so that it can be gathered conveniently at a high point within the assembly. Rather than mounting the collector assembly on the tower structure, as shown in FIG. 1, it may be desirable to employ an outer, downwardly extending skirt around the housing. Such a skirt assembly is designated by numeral 30 in FIG. 2. This skirt will collect any lighter-than-water fluid escaping from the housing in the same fashion as the conical structure shown in FIG. 1.

Means for transferring fluid from the collector assembly to the housing may include a pump and two or more conduits. Referring to FIG. I, conduit 31 is shown extending from the top of the collector assembly to platform 25 at the surface. Gravity flow through conduit 31 is insured by the difference between the specific gravities of water and the fluid contained in the collector assembly. A return reservoir 33 may be used to store fluid on or in proximity to the platform after it is conducted to the surface from the collector assembly. Pump 35 and conduit 37 are used to pump fluid from the return reservoir back to the housing. An auxiliary standby source of fluid is depicted as 39 and may be used to make up any losses incurred by the system. While the transfer means shown includes surface equipment it will be apparent that similar apparatus could be mounted on the ocean floor.

The apparatus of the invention normally will be installed on the buoyant tower before it is positioned on the ocean bottom. Housing 27 may be filled with fluid prior to installation ifa diaphragm, which may be temporary, is used to cover the open bottom and thus prevent fluid from escaping. Normally, however, the housing will be filled after the apparatus is installed. This is accomplished by feeding the fluid into tank 39 and using pump 35 to transfer the fluid to housing 27 via conduit 37. Placement of the proper volume of fluid into the housing can be assured by carefully gauging the volume pumped. ln lieu of this, fluid may be pumped in quantities sufficient to overflow the housing and establish a return flow from the collector assembly 29 through conduit 31 to the return reservoir 33. Establishment of return flow will insure that the housing is full of fluid.

While the apparatus of the invention has been discussed as embodied in a buoyantly supported tower, it will be apparent to those skilled in the art that it will also be useful in pro ctin and lubricating other unerwater structures. or e ample, It IS contemp ated that the apparatus of the invention will prove useful in conjunction with production risers employed to flare gas, with offshore risers, and with similar apparatus designed for service underwater for extended periods of time.

What is claimed is:

l. Offshore apparatus comprising:

a. a base provided with means for anchoring the same at the bottom of a body of water;

b. a rigid tower that extends upwardly from said base toward the surface of said body of water;

c. a pivot assembly interconnecting said tower and said base;

d. a buoyancy chamber attached to said tower near the upper end and positioned to remain at least partially beneath the water surface when the tower is installed in said body of water; and

e. a fluid-tight, open bottom housing attached near the lower end of said tower and extending downwardly about said pivot assembly to retain a lighter-than-water lubricating fluid around said pivot assembly as the tower sways in response to environmental forces.

2. Apparatus as defined by claim 1 including a means for collecting any of said fluid that escapes said housing, said means situated above said open bottom of said housing.

3. Apparatus as defined by claim 2 wherein said collecting means is a fluid tight outer skirt disposed about the perimeter of and extending downwardly from said bottom of said housing.

4. Apparatus as defined by claim 2 wherein said collecting means is a fluid tight, open bottom housing.

5. Apparatus as defined in claim 4 including means for transferring fluid from said collecting means to said housing.

6. Apparatus as defined by claim 5 wherein said transfer means includes a pump and at least one con duit. 

1. Offshore apparatus comprising: a. a base provided with means for anchoring the same at the bottom of a body of water; b. a rigid tower that extends upwardly from said base toward the surface of said body of water; c. a pivot assembly interconnecting said tower and said base; d. a buoyancy chamber attached to said tower near the upper end and positioned to remain at least partially beneath the water surface when the tower is installed in said body of water; and e. a fluid-tight, open-bottom housing attached near the lower end of said tower and extending downwardly about said pivot assembly to retain a lighter-than-water lubricating fluid around saId pivot assembly as the tower sways in response to environmental forces.
 2. Apparatus as defined by claim 1 including a means for collecting any of said fluid that escapes said housing, said means situated above said open bottom of said housing.
 3. Apparatus as defined by claim 2 wherein said collecting means is a fluid tight outer skirt disposed about the perimeter of and extending downwardly from said bottom of said housing.
 4. Apparatus as defined by claim 2 wherein said collecting means is a fluid tight, open bottom housing.
 5. Apparatus as defined in claim 4 including means for transferring fluid from said collecting means to said housing.
 6. Apparatus as defined by claim 5 wherein said transfer means includes a pump and at least one conduit. 